1. Field of the Invention
The present invention relates to a passive seatbelt system. In particular, it relates to a control circuit for a passive seatbelt system in which the conditions for the operation of the system are predetermined in accordance with the opening and closing of the door of a vehicle and whether or not the occupant is sitting in the seat of the vehicle, and a seatbelt is fastened around the occupant automatically by means of an electric motor.
2. Description of the Prior Art
In known systems of this type, it has been the practice to control the operation of the system by operating an electric motor in the forward and backward directions. This control method employs an electromagnetic relay and predetermined position detecting switches to directly switch on and off the driving current to the motor. The system of the above type has the following disadvantages. Firstly, since wires which have a current capacity required for driving the motor are employed in the wiring of seatbelt stopping position detecting limit switches, the occurrence of a short-circuit fault has the danger of causing a fire due to the large current capacity, and moreover the noise due to the operation of the electromagnetic relay is sensually offending. Further, while various measures have been attempted to overcome the problem of inertia of the moving parts including the motor which has heretofore been encountered in the designing of an automatic stopping mechanism used under conditions where the range of working temperature is wide and the voltage variation is great, they are all mechanical means so that their functions will be deteriorated by wear and it is not infrequent that these mechanical means are caused to vibrate by the chattering of seatbelt stopping position detecting limit switches. Further, since the control electromagnetic relay is mounted at a position different from that of a driving mechanism, a trouble is caused frequently about the wiring between the electromagnetic relay and the driving mechanism. Furthermore, the system is often housed in the door portion and therefore the electromagnetic relay is caused to operate erroneously by the shock due to the opening and closing of the door, thus giving rise to malfunctions of the system.